Design and Retrofit of Refinery Distillation Systems
Prof Robin Smith and Dr Megan Jobson
Abstract
This project has developed methodologies for the design and retrofit of heat-integrated distillation systems used for petroleum refining. For grass-roots and retrofit designs, the optimal set of operating conditions can be determined. Petroleum processes are often modified to accommodate increased throughput, changes in feedstocks, changes in product specifications and to improve energy efficiency. In such circumstances, the distillation system often needs extensive changes. This project develops procedures for cost-effective retrofit of refinery distillation sequences and heat-integrated distillation systems.
Project description
Distillation processes in petroleum refineries consume a significant portion of the energy demand of the site, in spite of extensive heat recovery. This research project addresses grass-roots and retrofit design of refinery distillation systems. Design is complicated by the complex distillation arrangements used, for example, for crude oil distillation, the highly inter-related heat recovery system, the use of steam as a stripping agent, and distillation under vacuum.
Process retrofits in the petroleum industries often require changes to be made to the distillation system. There are many ways in which existing distillation equipment can be utilised. Existing columns can have their internals modified. Feed conditions can be changed. Inter-reboiling and condensation can be added. Pump-arounds can be added or modified. The distillation sequence could be changed and/or columns reallocated to different separation duties. Pre-fractionators, post-fractionators or dephlegmators might be added to low temperature separations. Completely new columns might replace existing columns. Thermal coupling might be introduced or existing thermal coupling arrangements changed. Steam stripping arrangements can be modified, substituted with reboiling or reboiling substituted by steam stripping. Not only are there many options but the options can be combined in many different ways. This complex problem requires a systematic approach to ensure an optimal solution, without product yield or quality being compromised.
This project develops a systematic approach to the analysis and retrofit design of existing distillation systems. Methods developed for atmospheric distillation units are being extended to accommodate additional design complexities and for application to other distillation processes, such as the vacuum unit and FCC separation trains.